MySQL - Compare total this week against same week last year - mysql

Question

How would I get a sum of sales totals for the current week against the same week last year?
There are two possible scenarios related to how the dates are stored, as below:
Scenario 1
**Sales**
Date Sales
-----------------------
2012-08-10 11040.00
2012-08-09 11500.00
2012-08-08 14060.00
2012-08-07 93000.00
2012-08-06 11200.00
...
2011-08-10 11040.00
2011-08-09 11500.00
2011-08-08 14060.00
2011-08-07 93000.00
2011-08-06 11200.00
Scenario 2
**Sales**
year month day Sales
---------------------------------------------
2012 08 10 11040.00
2012 08 09 11500.00
2012 08 08 14060.00
2012 08 07 23000.00
2012 08 06 11200.00
...
2011 08 10 13040.00
2011 08 09 11500.00
2011 08 08 12060.00
2011 08 07 33000.00
2011 08 06 11250.00

Answer 1

For your first scenario, join against the same table on the WEEKOFYEAR() and one added to last year's YEAR():
SELECT
YEARWEEK(thisyear.Date) AS `YearWeek`
SUM(lastyear.Sales) AS LastYearSales
SUM(thisyear.Sales) AS ThisYearSales
FROM
Sales thisyear
LEFT JOIN Sales lastyear ON
WEEKOFYEAR(thisyear.Date) = WEEKOFYEAR(lastyear.Date)
AND YEAR(thisyear.Date) = (YEAR(lastyear.Date) + 1)
GROUP BY `YearWeek`
The second scenario requires building a date out of the 3 separate values. I think this will work:
SELECT
YEARWEEK(CONCAT_WS('-', thisyear.year, thisyear.month, thisyear.day)) AS `YearWeek`,
SUM(lastyear.Sales) AS LastYearSales,
SUM(thisyear.Sales) AS ThisYearSales
FROM
Sales thisyear
LEFT JOIN Sales lastyear ON
WEEKOFYEAR(CONCAT_WS('-', thisyear.year, thisyear.month, thisyear.day)) = WEEKOFYEAR(CONCAT_WS('-', lastyear.year + 1, lastyear.month, lastyear.day))
GROUP BY `YearWeek`